Step-up/step-down voltage converter with bipolar synchronous rectification element

Abstract

A DC/DC conversion circuit, adapted to convert a DC input voltage to a DC output voltage, employs a PNP type of bipolar power transistor as a synchronous rectifier element, to allow power-on through a simplified control circuitry capable of sensing, automatically and at a high speed, the difference of potential across the switch. This approach allows power to be transferred from the input to the output unilaterally, while automatically controlling the depth of saturation of the power transistor and regulating its base current.

What is claimed is: 
     
       1. A DC/DC conversion circuit having at least one input terminal and an output terminal, and being adapted to convert a DC input voltage to a DC output voltage, which circuit comprises: an inductor adapted to transfer energy from said input terminal to said output terminal;   a capacitor connected to the output terminal for storing energy transferred from the inductor;   a first electronic switch coupling the inductor to a reference voltage;   a second electronic switch coupling the inductor to the output terminal, wherein the second electronic switch has at least a first terminal connected to a terminal of the inductor and has a second terminal coupled to the output terminal of the converter, and comprises a power transistor having a main conduction path connected between said first and second terminals and a control circuit which senses a difference of potential between said first and second terminals and drives the power transistor, wherein the control circuit comprises a drive block adapted to drive the power transistor and a compare block supplying an enable signal to the drive block, which compare block has at least three input terminals connected to said first terminal, said second terminal, and said input terminal of the control circuit, respectively.   
     
     
       2. A circuit according to claim 1, wherein the compare block enables the drive block upon a potential at the first terminal exceeding a potential at the second terminal. 
     
     
       3. A circuit according to claim 2, wherein the power transistor is a PNP type of bipolar power transistor. 
     
     
       4. A circuit according to claim 1, wherein the compare block enables the drive block upon a potential at the first terminal exceeding a potential at the second terminal, if the DC input voltage is equal to or below the DC output voltage, or upon the potential at the first terminal exceeding the potential at the input terminal of the control circuit, if the DC input voltage is above the DC output voltage. 
     
     
       5. A circuit according to claim 4, wherein the power transistor is a PNP type of bipolar power transistor. 
     
     
       6. A DC/DC conversion circuit, comprising: an input terminal at which a DC input voltage is present;   an output terminal at which a DC output voltage is produced;   an inductor coupled to the input terminal;   a first power transistor having a control terminal, a first terminal coupled to the input terminal via the inductor, and a second terminal coupled to the output terminal; and   a control circuit having first and second input terminals coupled respectively to the first and second terminals of the first power transistor, and an output terminal coupled to the control terminal of the first power transistor, the control circuit being structured to drive the first power transistor based on a difference in potential between the first and second terminals of the first power transistor, wherein the control circuit includes a third input terminal coupled to the input terminal of the conversion circuit.   
     
     
       7. The conversion circuit of claim 6, further comprising a capacitor coupled to the output terminal of the conversion circuit to store energy transferred from the inductor via the first power transistor. 
     
     
       8. The conversion circuit of claim 6, further comprising: a second power transistor having a control terminal, a first terminal coupled to the inductor and the first terminal of the first power transistor, and a second terminal coupled to a reference voltage; and   a timing circuit coupled to the control terminal of the second power transistor and thereby provide timing for coupling the inductor to the reference voltage.   
     
     
       9. The conversion circuit of claim 6 wherein the control circuit includes a drive block structured to drive the first power transistor and a compare block that senses the difference in potential between the first and second terminals of the first power transistor and provides an enable signal to the drive block when a potential at the input terminal of the conversion circuit exceeds a potential at the output terminal of the conversion circuit. 
     
     
       10. The conversion circuit of claim 6 wherein the control circuit includes a drive block having an input terminal and output terminal coupled to the control terminal of the first power transistor and a comparator having an output terminal coupled to the input terminal of the drive block, a first input terminal coupled to the first terminal of the first power transistor, a second input terminal coupled to the second terminal of the first power transistor, and a third input terminal coupled to the input terminal of the conversion circuit. 
     
     
       11. The conversion circuit of claim 10 wherein the comparator includes a first transistor coupled between the first input and output terminals of the comparator; a second transistor having a control terminal coupled to the second input terminal of the comparator, a first terminal coupled to a control terminal of the first transistor, and a second terminal; and a third transistor having a control terminal coupled to the third input of the comparator and first and second terminals respectively coupled to the first and second terminals of the second transistor. 
     
     
       12. The conversion circuit of claim 11 wherein the comparator includes a current generator coupled between the second terminal of the second transistor and a reference voltage and the drive circuit includes a Darlington switch having a control terminal coupled to the output terminal of the comparator, a first terminal coupled to the reference voltage, and a second terminal coupled to the output terminal of the drive circuit. 
     
     
       13. The conversion circuit of claim 12 wherein the drive circuit includes a capacitor coupled between the first input and the output terminals of the comparator. 
     
     
       14. A method of providing DC/DC conversion between a DC input voltage at an input terminal and a DC output voltage at an output terminal using a conversion circuit having an inductor and a switch coupled between the input and output terminals and coupled to each other at an intermediate node, the method comprising: sensing a voltage at the intermediate node;   comparing the intermediate node voltage with the output voltage;   comparing the input voltage with the output voltage; and   closing the switch to electrically connect the inductor with the output node based on the comparison steps.   
     
     
       15. The method of claim 14 wherein the closing step includes closing the switch to electrically connect the inductor with the output node if the input voltage exceeds the output voltage and the intermediate node voltage exceeds the input voltage. 
     
     
       16. The method of claim 14 wherein the closing step includes closing the switch to electrically connect the inductor with the output node if the input voltage does not exceed the output voltage and the intermediate node voltage exceeds the output voltage. 
     
     
       17. A circuit according to claim 1 wherein the compare block includes an output terminal at which the enable signal is produced, a first transistor coupled between the first input and output terminals of the compare block; a second transistor having a control terminal coupled to the second input terminal of the compare block, a first terminal coupled to a control terminal of the first transistor, and a second terminal; and a third transistor having a control terminal coupled to the third input of the compare block and first and second terminals respectively coupled to the first and second terminals of the second transistor. 
     
     
       18. A circuit according to claim 17 wherein the compare block includes a current generator coupled between the second terminal of the second transistor and a reference voltage and the drive block includes an output terminal coupled to a control terminal of the power transistor, a Darlington switch having a control terminal coupled to the output terminal of the compare block, a first terminal coupled to the reference voltage, and a second terminal coupled to the output terminal of the drive block.